This invention relates to an optical switching apparatus for switching optical waveguides, from one to another.
A variety of optical communication systems have been developed. Optical switching apparatus of various types have been invented, which may be used in the optical communication systems.
An optical switching apparatus is disclosed in, for example, Japanese Patent Disclosure No. 56-27103 and U.S. patent application Ser. No. 65,667 (now abandoned) which corresponds to the Japanese patent disclosure and which was filed on Aug. 1, 1979 by E. J. Rawson. The optical switching apparatus comprises a pair of input optical fibers and a pair of output optical fibers. The output fibers are fixed to a stationary block, and the input fibers are fixed to a movable block. As long as the movable block stays in a first position, the input fibers are optically connected to the output fibers, respectively. When the movable block is moved to a second position, only one of the input fibers is optically coupled to one of the output fibers. The apparatus is designed for used in only one specific optical communication system. It cannot work if incorporated into other optical communication systems. It can change only two-input/two-output state to one-input/one-output state, or vice versa.
An optical switching apparatus which may be used in optical communication systems of different types is disclosed in Japanese Patent Disclosure No. 54-13349. The apparatus comprises a first input optical fiber and a second input optical fiber both fixed to a first stationary block. It further comprises a first output optical fiber and a second output optical fiber both fixed to a second stationary block. Between the stationary blocks a movable block is so disposed that a first gap is provided between the first stationary block and the movable block and a second gap is provided between the second stationary block and the movable block. The movable block holds four coupling optical fibers.
As long as the movable block lies in a first position, one end face of the first input fiber faces one end face of the first coupling fiber through the first gap, and the other end face of the first coupling fiber faces one end face of the first output fiber through the second gap. Similarly, in this state, one end face of the second input fiber faces one end face of the second coupling fiber through the first gap, and the other end face of the second coupling fiber faces one end face of the second output fiber. Therefore, an optical signal supplied through the first input fiber is transmitted to the first output fiber and an optical signal supplied through the second input fiber is transmitted to the second output fiber through the second coupling fiber.
When the movable block moves to a second position, the end face of the first input fiber comes to face one end face of the third coupling fiber through the first gap, and the other end face of the third coupling fiber comes to face the end face of the second output fiber through the second gap. At the same time, the end face of the second input fiber comes to face one end face of the fourth coupling fiber through the first gap, and the other end face of the fourth coupling fiber comes to face the end face of the first output fiber through the second gap. Therefore, as long as the movable block stays in the second position, an optical signal supplied through the first input fiber is transmitted to the second output fiber through the third coupling fiber and an optical signal supplied through the second input fiber is transmitted to the first output fiber through the fourth coupling fiber.
The optical switching apparatus disclosed in the Patent Disclosure No. 54-13349 is manufactured in the following manner.
First, four optical fibers are adhered on a rectangular flat plate and arranged thereon in a specific manner. On one end portion of the plate the first and third optical fibers extend straight and parallel and lie close to each other. On the same end portion the second and fourth fibers extend straight and parallel and lie close to each other. On the intermediate portion of the plate the third fiber curves, intersecting first with the first fiber which is straight. On the intermediate portion of the plate the fourth fiber curves, intersecting first with the third fiber at about the center of the plate and then with the first fiber. On the other end portion of the plate the first fiber and the fourth fiber extend straight and parallel and lie close to each other, and the second and third fibers extend straight and parallel and lie close to each other. The rectangular plate with the four fibers is then cut into three rectangular blocks, a first stationary block, a movable block and a second stationary block. The edge of each block is polished and cleaned. This done, the first and second stationary blocks are fixed to a base, spaced from each other. The movable block is laid on the base and between the first and second stationary blocks, with a first gap between it and the first stationay block and a second gap between it and the second stationay block. Thus is completed the optical switching apparatus disclosed in Japanese Patent Disclosure No. 54-13349.
The optical switching apparatus of Patent Disclosure No. 54-13349, however, is disadvantageous in the following respects:
(1) The rectangular flat plate must be cut twice, thereby to provide three blocks. Four parallel edges of the blocks thus provided must be polished. Much time is necessary to cut the plate into three blocks and to polish each block, inevitably raising the cost of the apparatus. In addition, technical difficulties envolve in polishing the four edges of the blocks truly flat and truly parallel to one another.
(2) The coupling fibers intersect at three points. Therefore, the coupling fibers may be cut in the manufacturing process. To avoid such a problem, the apparatus has to be large.
(3) The gaps between the blocks must be extremely uniform. It is therefore time-consuming to arrange the three blocks to provide such uniform gaps. This would raise the cost of the apparatus. Unless extremely uniform gaps are provided, a great power loss will be unavoidable.
(4) Either gap, i.e. the distance between the movable block and either stationary block, may change as the ambient temperature rises and falls. Provided with two gaps, the apparatus has worse temperature characteristics.
(5) The optical fibers are longitudinaly arranged. The switching apparatus may be relatively large.